Field
The following description relates to a control of a voltage imbalance in a direct current (DC) distribution system.
Description of Related Art
In traditional alternating current (AC) power distribution, digital devices having direct current (DC) loads are supplied power through a DC power adapter that converts the alternating current (AC) power. Also, battery-based power storage and photovoltaic generation use or provide DC power that must be converted to or from AC power for transmission or reception via the traditional AC distribution system.
Direct current (DC) distribution is suitable for digital devices, battery-based power storage devices, and photovoltaic generation devices because they operate using DC power. DC distribution has been applied to large-scale data centers with an abundance of DC loads, and to photovoltaic generation-based facilities that generate DC power.
DC distribution technology advantageously eliminates concerns related to AC distribution, such as reactive power, power factor, frequency, and electromagnetic radiation. Further, DC distribution technology also has the advantage of enabling DC power to be directly stored and used. Conversely, AC distribution technology needs to convert AC power into DC power for storing energy and to change the stored energy from DC power to AC power while taking into account frequency and phase for using the stored energy. Low-voltage direct current (DC) distribution systems are classified into unipolar systems and bipolar systems. A unipolar system supplies single common DC voltage via a positive line (+) and a negative line (−) to all loads. A bipolar system is a system where a load point is provided with two DC/DC converters. A first DC/DC converter uses the positive line (+) and the neutral line (NT) to supply a first DC voltage to a first load and a second DC/DC converter uses the neutral line (NT) and the negative line (−) to provide a second DC voltage to a second load. A bipolar system is more stable than a unipolar system because even when loads on one line, the positive line (+) or the negative line (−), suffer from a fault, such as a short circuit, loads on the other line, the negative line (−) or the positive line (+), are not influenced.
At each load point in a bipolar system, a first load current flows to the neutral line from a consumer load, which receives the first DC voltage between the positive line (+) and the neutral line (NT). In the same manner, a second load current flows to the neutral line (NT) from another consumer, which receives the second DC voltage between the neutral line (NT) and the negative line (−). If the loads of the first and second consumer at the load point are balanced, the first load current and the second load current are desirably balanced in the neutral line. This results in a minimal net current flow in the neutral line, which prevents a voltage drop from occurring due to the impedance of the neutral line. However, even if the loads connected to the positive line (+) and the negative line (−) are initially balanced, the magnitude of the loads will change over time causing an unbalanced current between the positive line (+) and the negative line (−). The unbalanced current leads to the neutral line receiving higher current and causes the voltage of the neutral line (NT) to shift due to the impedance of the neutral line (NT). The voltage shift of the neutral line (NT) creates a voltage unbalance between the positive line (+) and the negative line (−).
Therefore, there is a need for a technique capable of reducing the influence of load unbalance in DC distribution technology.